1. Field of the Invention
The present invention relates to methods for preparation of photoresist compositions and, more particularly, to formulation of photoresists in a one-pot procedure as well as other methods for improved resist manufacture.
2. Background
Photoresists are photosensitive films for transfer of images to a substrate and form negative or positive images. After coating a photoresist on a substrate, the coating is exposed through a patterned photomask to a source of activating energy such as ultraviolet light to form a latent image in the photoresist coating. The photomask has areas opaque and transparent to activating radiation that define a desired image to be transferred to the underlying substrate. A relief image is provided by development of the latent image pattern in the resist coating. The use of photoresists is generally described, for example, by Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York (1975), and by Moreau, Semiconductor Lithography, Principals, Practices and Materials, Plenum Press, New York (1988).
Current practice provides that photoresists and the components thereof are prepared in multiple step procedures. For example, each of the components of a photoresist composition--such as a resin binder component and photoactive component--are separately prepared and isolated then admixed in a photoresist solvent to prepare the liquid coating composition. Thus, for example, in current practice, a resin binder component is synthesized and then isolated from the reaction solvent. The isolated solid resin material is then typically washed with a non-solvent such as water and dried prior to being dissolved in a photoresist solvent to prepare the resist formulation.
Such a multi-step process can present notable shortcomings. For example, a multiple step procedure can pose significant engineering challenges, particularly for large scale resist production, as well as add substantially to manufacturing costs.
Impurities present in photoresist components also can present problems. For example, soluble impurities such as moisture may be present from the manufacture of resist components and from the packaging containers or dispensing tanks. Such impurities can render a photoresist unsuitable for its intended purpose, e.g. damage an integrated circuit manufactured with the resist.
It thus would be desirable to have new methods for preparation of photoresist compositions. It would be particularly desirable to have new production methods that reduce the steps required to produce a resist. It would be further desirable to have new methods for producing photoresists of enhanced purity.